Cellular telephone manufactures strive to continually provide new and innovative services in an attempt to keep existing customers and draw in new customers in an industry that is already very competitive. Location based services enable personalized services to be offered based on a person's (or item of the person) location. Services include, for example, areas of security, E911 services, selective advertising services, fleet and resource management, location based information, vehicle tracking, person-to-person location, and messaging applications.
Location-based information services allow subscribers to access information for which the information is filtered and tailored based on the location of the requesting user. Service requests may be initiated on demand by subscribers, or automatically, when triggering conditions are met, and may be a singular request or result in periodic responses. Examples of location based information services include the following: navigation to guide the user to his or her destination; city sightseeing to describe historical sights, find restaurants, the airport, bus terminal, etc.; location dependent content broadcast, that support broadcasting content to a user in a certain geographical area; and, mobile yellow pages, for finding telephone numbers and addresses, for example.
Additionally, federal law requires that all Personal Communications System networks and mobile communications networks be capable of providing location information for wireless calls made to emergency services. Under Phase II of the Federal Communications Commission wireless E911 mandate, it is required that technology be in place such that a dispatcher can know more precisely where the caller is located, a capability called Automatic Location Information.
One method of determining the location of a wireless caller is by Time Difference of Arrival (TDOA) technology. The TDOA technique works based on triangulation by measuring the time of arrival of a mobile station radio signal at three or more separate cell sites. In a cellular system using TDOA, a caller will place a call that is received at several base station transceivers (BTS), although only one BTS is assigned by the network to provide cellular communications service to the caller. A BTS is part of a BSS (Base Station Subsystem), which BSS includes the BTS and a BSC (Base Station Controller). Each BTS receiving the call signal will pass it through the BSC to a MSC (Mobile Switching Center).
The MSC is part of an NSS (Network and Switching Subsystem), and is a cellular central office that can perform all switching and signaling for cellular telephones in the MSC's area by routing calls between the mobile network and the fixed telephone network (e.g., the PSTN-Public Switched Telephone Network). TDOA equipment at the MSC will determine the difference in time that the signal arrived at each of three or more BTS sites and calculate the latitude and longitude of the caller based on the time difference and triangulation. The MSC then forwards the call, along with the caller's location, to the requestor.
One current method of implementing TDOA location technology in wireless networks requires that the BTS have the capability to determine timing information for received signals. In support thereof, a Wireless Location Sensor (WLS) can be located at each BTS. The WLS measures features of the wireless mobile station radio signals and transmits the call signal information to a Geolocation Control System (GCS) that is also located at the MSC. The GCS is a central location processor that manages, coordinates, and administers the WLS network. The GCS converts the radio signal information received from the WLS into latitude/longitude data and communicates the data to the PSAP for deployment of services. However, providing a WLS at each BTS is very expensive due to equipment, installation, and maintenance costs.
Another method of location measurement requires a large number of existing cell sites. In this method, at least 5-10 mathematical contributors are needed to get an accurate measurement for location determination. Accuracy is not significantly improved with over 10 mathematical contributors. The mathematical contributors utilize TDOA technology and take measurements of the timing differences between signals received at each of the cell sites to triangulate the mobile subscriber's position. Accordingly, this method is only useful in suburban areas where a large concentration of cell sites exist. Sparsely populated areas, where there are limited cell sites have no accurate means of determining the location of a wireless caller.
Accordingly, there is an unmet need for an improved wireless caller location system for use in sparsely populated areas, as well as suburban areas. Such a system will give accurate readings of location measurements without the need for additional cell sites and is cost effective with updating and replacing existing structures.